For a conventional fuel supply pump, there is a pump including a low-pressure pump that pumps up fuel from a fuel tank; and a high-pressure pump that includes a pressurizing chamber, to which the fuel from this low-pressure pump is supplied, and that pressurizes the fuel in the pressurizing chamber. The high-pressure pump includes a cam shaft rotated by an internal combustion engine; and a cam that is provided eccentrically to the central axis of the cam shaft and that is rotated integrally with the cam shaft. The fuel in the pressurizing chamber is pressurized by a plunger which is driven by the cam.
As illustrated in FIG. 11, a cam shaft 101 is bearing-supported by a bush 103 which is fixed to a housing 102. Accordingly, if a heat release between the cam shaft 101 and the bush 103 is insufficient, a sliding surface between the cam shaft 101 and the bush 103 may be seared. Particularly, as illustrated in FIG. 11, heat is not easily released from a central part of the bush 103 in its axial direction.
Accordingly, in JP-A-2004-270647 corresponding to U.S. 2004/0179950A1, there is disclosed a technology for cooling the bush 103 by forcibly flowing a part of fuel discharged from a low-pressure pump using feed pressure into a clearance 104 between the cam shaft 101 and the bush 103.
However, according to the technology described in JP-A-2004-270647, the fuel passing through the clearance 104 flows into a cam chamber 105 to be returned to a fuel tank. Thus, a part of fuel that is supposed to be discharged from the low-pressure pump and to be supplied into a pressurizing chamber is lost. As a result, the amount of fuel discharged from the low-pressure pump is reduced, and startability of the fuel supply pump may thereby deteriorate.